# Simulation CFD

#### Symmetry and some questions

82 Views, 6 Replies
03/07/2018 10:26 AM

hi, sorry for the following mess

if i have flow inside a pipe and want to use symmetry condition,

divide the pipe from the have, shall divide the mass flow rate by 2 ?

if i have heat flux on the pipe surface, shall i divide the real heat flux value by 2 also?

at meshing what is the recommended wall layer number, is it 10 as in external force flow?

if i have multiphase flow in the pipe to find the quality at the output, what are bulk values i need

to use to find the quality?

what kind of thermal table do i need to use ?

http://help.autodesk.com/view/SCDSE/2018/ENU/?guid=GUID-FAF6581B-5FFB-4BAB-91DF-10BA8D35CC62

if i add entry length and don't want to add any heat from the pipe surface to this length what to do?

you can check the cfz file:

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#### Re: Symmetry and some questions

03/07/2018 11:31 AM

Hi!

eng.abass5 wrote:

if i have flow inside a pipe and want to use symmetry condition,

divide the pipe from the have, shall divide the mass flow rate by 2 ?
yes

if i have heat flux on the pipe surface, shall i divide the real heat flux value by 2 also?
no, if its W/m^2

at meshing what is the recommended wall layer number, is it 10 as in external force flow?
experts say 5 i think. 10 is better more elements?

if i have multiphase flow in the pipe to find the quality at the output, what are bulk values i need

to use to find the quality?
no idea

what kind of thermal table do i need to use ?

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Message 2 of 6 ( Views: 76 )

#### Re: Symmetry and some questions

03/07/2018 11:59 AM

thank you

why when i use very fine meshing setting i can't notice any variation in temperature of the pipe or the fluid

( heat flux at the outer surface of the pipe )

just hot spots at the entrance, this was after running 5 iterations which took more than 20 hours.

but it is ok when i use coarser mesh setting !

is there any good meshing practice in case of multiphase?

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Message 3 of 6 ( Views: 72 )

#### Re: Symmetry and some questions

03/07/2018 12:03 PM

Hi

20 hours for 5 iterations is crazy much.. Try using adaptive meshing?

maybe put heatflux at the inside of the tube? or just on the outside of the water? thought it is weird it dosn't take/add heat from the water as it is now

isak

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#### Re: Symmetry and some questions

03/07/2018 12:37 PM

hi i ran you simulation with very course mesh, and all your stuff, seems its taking heat from the water;

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Message 5 of 6 ( Views: 63 )

#### Re: Symmetry and some questions

03/07/2018 1:47 PM

yes, i have the same problem!

fluid here is a saturated refrigerant ,not water.

also i noticed that the velocity is very high , about 150 m/s !!

is there any thing wrong about heat flux boundary condition at pipe surface ?

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